This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2003-10735, filed Jan. 20, 2003, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The invention relates to a detector of near-infrared light.
2. Description of the Related Art
The detection of near-infrared light is applied to, for example, environmental measurement, such as the measurement of water droplets, dust in the atmosphere and the like, the detection of gas and the analysis of trace materials in various industrial fields. It is thought that the detection of near-infrared light will be applied further to medical diagnosis and the like in the future.
To be specific, there has been carried out measurement of fine particles by scattering in the atmosphere by the use of an infrared laser (observations of weather and the observations of air pollution by the distribution of cloud, fog, and the like). The size of the particles observed in this measurement depend on the wavelength of the infrared laser. For this reason, a high sensitivity device capable of detecting near-infrared light after passing through the atmosphere is needed in order to broaden the scope of measurable objects and to enable more detailed observation.
Further, trace materials can be analyzed by utilizing the fact that near-infrared light easily passes through animals and plants and that bodies absorbing molecules having functional groups including hydrogen (OH, NH, CH, and the like) exist in a near-infrared region. For this reason, similarly, it is desired to develop a detector of near-infrared light having high sensitivity.
Incidentally, feeble light is generally detectable by the use of a photodetector, such as photomultiplier tube or the like. However, a detector having high sensitivity for light in the near-infrared region does not exist, therefore it is desired to be developed.
As a detector of near-infrared light, one has been known that uses a light-emitting diode (avalanche photo diode) as a light receiving device and applies an electron multiplication action in the diode to the measurement of the number of photons of near-infrared light. However, in this detector, the light receiving device needs to be cooled in order to reduce noise and to amplify an S/N ratio and hence presents a problem that it has a complex structure.
On the other hand, in Jpn. Pat. Appln. KOKAI Publication No. 2000-74737 is disclosed a photodetector that has a high-frequency oscillator, a cavity resonator, a magnet for modulating a magnetic field, and a light-detecting part made of (Pr, Ca) MnO3 and sweeps the magnetic field while applying a constant frequency thereby to detect a change in electron spin in the (Pr, Ca) MnO3 as feeble light (for example, near-infrared light) with an ESR (electron spin resonance) measurement instrument.
However, the photodetector disclosed in the above-mentioned patent gazette has an operating temperature of a liquid nitrogen temperature or lower of from 50 K to 80 K and thus needs to be provided with a cryo-cooler. As a result, the photodetector is problematic, in terms of having a complex structure and being increased in size, which not only increases cost but also limits the usability.
The object of the invention is to provide a photodetector of near-infrared light that can detect near-infrared light at room temperature, with high sensitivity.
According to the invention, there is provided a detector of near-infrared light comprising:
a light receiving device having a perovskite-type composite oxide expressed by a general formula of La1-xPrxCrO3 (where 0 less than x less than 1); and
magnetization measuring means for measuring an increase in magnetization in the composite oxide of the light receiving device when the light receiving device is irradiated with near-infrared light at room temperature.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.